For over-riding operational reasonsthese instructions can be ignored, but explanatory form must be completed

16Getting everybody involved is essential - everyone has different motivations 17Motor Management Policy at North West Water

Get Senior Management on your side - and get everybody to buy in

Be prepared to overcome the obstacles in your way - and to see through changes in the way things are done

Consider shifting responsibility by Contracting out.

Pace yourself for a long slog - and try not to lose heart half way

The energy saving benefits alone make it very worthwhile

18Is speed control right for you?

Before deciding to alter the speed, make sure that you understand the system. Otherwise you could make things worse!

If the machine can always turn at a lower speed, then you could alter the speed in many ways, you dont have to use a VSD.

However, as the price of VSDs gets lower, they are being used in more and more applications

19Why do we want to control speed?

Being able to alter the speed of a fan, pump, conveyor, machine tool, gives us tremendous opportunities to better control the process.

In some applications, it can also save lots of energy.

There are lots of ways to control the speed of a machine, not just the VSD!

20Altering the flow by using sequencers

In some circumstances it makes more sense to switch machines on/off to match the flow to the demand.

Common examples are pumps or air compressors

21Fan Affinity Laws (Applies to all centrifugal loads)

Flow proportional to the speed

Pressure proportional to the speed squared

Power proportional to the speed cubed

22Inherent VFD Benefits

Controls speed variations

Provides mechanical control

Eliminates startup impacts causing system vibration

Provides fault tolerance

Supports soft starts

Restarts spinning load

Controls speed swings

Enhances product quality

Conserves energy

Repeats results

23Getting the Economics right

Look for applications where you can reduce the speed by at least 20

Look for applications operating at least 4,000 hours pa

Watch out for applications with high static head

24Important Considerations for Variable Speed Drives

Engineering analysis required for each unique application

Load profile of the driven equipment must be evaluated over the full range of operating conditions

Effect of reduced speed on torque

Affinity laws apply for frictional pump systems, but not for static head-dominated systems

25Methods of control

AVSD is only as good as the way it is commissioned.

There are two methods of control

Open Loop. The speed is simply controlled by a potentiometer. The speed is set either by a person, or perhaps by simple controls allowing perhaps 2-4 speeds, depending on the situation.

Closed Loop. This is much more powerful, with the user setting the flow, temperature, pressure, or whatever else it is that they want to control. Using a sensor, the VSD adjusts the speed automatically to maintain this parameter. This will always give optimum results, as long as it is set up properly!

26How good are your controls?

Was it properly commissioned?

How were the settings decided on?

How much safety margin have you got?

How quick does your system respond?

How good are your sensors?

Has anyone altered the settings?

Has it been switched to manual?

27De-rating of Motors

Because the generated waveform is not a smooth sinusoid, there is additional heating within the motor.

In the past this has meant de-rating the motor by up to 10

With more modern PWM VSDs working at higher switching frequencies, the waveforms are much cleaner, and so the de-rating is much less.

Some manufacturers claim that you dont have to apply any de-rating at all - but always check first

In practice, with centrifugal loads, the power goes down so fast with speed, that just a small reduction in speed will compensate for the additional heating due to a poor waveform

28To categorize by motor size and run time, don't we need to do a plant-wide inventory?Prescreening Motor Systems - getting at the VITAL FEW

Not only do we not need it, it would be the WRONG thing to do

The first level of screening - by size and run time - should be a one day effort for many plants

Plant operations involvement is essential

29Where to look

At many sites the main production equipment is well maintained, and so there is not much opportunity for making changes. Also the costs of downtime might be too high!

Look instead at the backroom services. These are often neglected, running long hours and badly matched for current demand patterns. They also have big motors, and lots of opportunity for better controls such as VSDs or sequencers

This will take time and money, so think carefully what you need to know

Dont collect more data than you need

Never collect data because it may be useful one day

The objective of data collection is to refine your estimate of the cost effectiveness of an energy saving measure so that you are confident that you should, or should not, do it.

And dont forget to take measurements once the energy saving measure has been fitted. This way you can tell everybody how clever you are!

33Estimating power without taking any electrical measurements

Measuring the speed of the motor with a stroboscope can give a useful indication of motor power - ideal for initial screening

Accuracy of perhaps /- 20

Very Quick!

34The slip method of estimating motor power

This is based on the fact that the torqueslip characteristics in the normal operating region of an induction motor are very straight. So, at full rated load the motor will be at its maximum slip (and hence minimum speed.) By comparing the actual measured speed with the nameplate rated slip, the power can be estimated.

Youll struggle to save energy and not reduce maintenance costs, and vice versa. 38Perspectives on a Site Energy Audit

The Energy Manager - Sees equipment as consumers of energy

The Salesperson - Keen to show the latest technology

The Production Manager - Reliability and performance of the plant

The Maintenance Engineer - The costs of maintaining plant and related on-going problems

39Understand the system

Whether youre trying to sort out a maintenance problem or are looking for energy savings, you need to understand how the equipment works.

Just by listening to the accounts of everyone with an interest in the equipment, you can soon get very good clues as to what is going on.

Dont jump in and just try to fix the reported problem, find out about the whole related system. 40Surplus energy is the root cause of many Maintenance problems

Energy Used 100kW x 24 hours 2400kWh per day

Useful Work done (assuming 60 efficiency)

1140kWh. Where does the 960kWh go!?

It is this surplus energy, ie energy that is doing nothing useful, that causes maintenance problems. Principally Direct heat, friction and their resultant effects. Equipment that is 100 efficient has no surplus energy for causing maintenance problems. 41Getting it together - the benefits of integrating Maintenance and Energy savings

Dont make an issue of it, make energy saving projects a matter of policy

Assess the non-energy saving benefits, the paybacks are better and you get more support

Look to integrate energy saving in to higher management concerns

Is it set up right - are you sure?

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